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MG Midget and Sprite Technical - Adjustable cross rods
|Does anyone know who supplies adjustable cross rods for 1970 midget. I need to get my handbrake to work, and have taken up all the other adjustment points to their maximums. (Mot looms.....)|
|I made my own. I cut the ends off the rods, tapped a thread, and fitted clevis ends.|
|I'm pretty sure there's stuff in the archive about this; IIRC the Moss ones are adjustable as standard because it saves them having different parts for steel wheel and wire wheel axles.|
|Thanks David. I've had a look on their website and you are correct - they do offer adjustable ones. Methinks I'll go that route. Thanks again.|
Before you go buying new parts, check the mounting plate for your handbrake lever. I started a thread about brake adjustment a month or two back but in the end the problem turned out to be a cracked mounting plate - apparently it's quite a common fault. I managed to cure mine with a bit of welding. The handbrake is now working fine with plenty of adjustment left.
|The Moss rods work fine, but be aware that if you need to extend the thread it isn't the 1/4" UNF that you'd think it is.|
One other thing to check before changing the rods is how far out from the backplate is the lever to which the cross rod attaches. It should be right back against the backplate for optimum geometry. Frequently there is a gap approaching half an inch or more. If that's the case check:
* adjustment of shoes, having first removed the clevis pin securing the cross rod (sounds like you have already done this)
* linkages/levers in the drum for wear (they do)
* brake drum for wear (very common)
When, at handbrake take-up point, the lever is more than 5mm from the backplate then braking efficiency will be impaired, and the further out it gets the less the mechanical advantage transmitted to the shoes.
Wear in the drum levers/linkages is easily addressed by welding to build up the base of the notches which engages the shoes and dressing off. (Don't forget to measure where the old notch's base was before welding!)
To an extent, this process can also be used to overcome a bit of wear in the drum, but well worn drums should always be replaced - especially Midget ones as I have seen them crack between rim and centre. The max drum oversize should be embossed inside the drum, if not then use +.060" as a replacement figure.
Once the correct take-up situation is achieved, there is one remaining obstacle in the way of a good handbrake: in the Midget set-up, the leading shoe is not activated directly by the primary lever (the one to which the cross rod is attached), but instead is actuated by the secondary lever - the one which runs across underneath the wheel cylinder to the other (leading) shoe. This secondary lever is dragged onto the backplate by the pull of the cross rod on the primary lever.
The resulting friction between backplate and secondary lever absorbs some of the effort that's transmitted to the leading shoe - sometimes it can be quite a lot. We have addressed this by deepening and re-shaping the notch in the primary lever which engages with the shoe so that the sideways thrust is then taken by the primary lever hanging on the shoe, in conjunction with grinding the inner edge of the secondary lever to give more clearance from the backplate.
The things you learn from decades of autotesting where an efficient handbrake is paramount!
That was the best artical ive seen on rear midget brakes...that need to be published in the Moss catologe or the (mogc ???) magizine
im making a copy of that
agian ...thank you
|Prop and the Blackhole Midget|
|Paul, is there any chance of an explanatory picture of the mod|
Better to see it than to imagine it and it sounds as if your mod will be ideal for Geoff as well
Geoff, if you need the bracket welding let me know
|As I said Prop, autotesting makes you very conscious about handbrake efficiency!|
Bill - good idea, though I only have this rather rough sketch and nothing easily accessible to photograph at the moment. References on the diagram are:
1. Max gap here at take-up of handbrake about 5mm
2. Build up notches to compensate for linkage wear.
3. To increase load transmission to the leading shoe, add metal here onto primary lever to provide a firm footing to take the reaction force of the sideways pull on the rod. In doing so, ensure that the built up bit has an approx wedge-shaped gap between it and the shoe (as shown) to allow for the rocking action of the lever as it is actuated. The contact face of the built up bit should have an appropriate radius to allow this rocking action and keep proper contact with the shoe. Check when finished that it doesn't jam.
4. Cut off this extension of the secondary/transfer lever. It's presence encourages binding by the scissor-action of the two levers on the shoe. If this happens, much of the handbrake pull goes into clamping the shoe between these tow and not on pushing the shoes apart!
5. Grind the inside edge of the transfer lever to gain clearance from backplate, thus eliminating frictional drag which reduces the effort transferred to the leading shoe.
Then smile at how much better the handbrake works!!
|Thanks Paul, I'll give this a shot this week on Lara who, God bless her, could do with all the handbrake assistance she can get.|
My drive is about one in three.
|The other thing that I have not seen mentioned, but that does make a difference, is the positioning of the "christmas tree" lever arrangement between the cable and the rods. It is important that this is orientated correctly so that as far as possible the rods attach to the lever arm on the tree at right angles at the point that the handbrake begins to bite. This means that the angles will not be 90 degrees when the handbrake is released, but will come to around 90 degrees as it is pulled on to its holding point. At this point, the cable and its lever arm will also be near enough to 90 degrees. This will give the best leverage and tension transfer between the cable and the rods.|
Sorry about the words, a sketch would have been easier!
|Is the late 1500 setup better? (the one with the floating tension rod)|
|Thanks Guy, I meant to mention that too but forgot. In particular, if the "tree" turns too far past the 90 deg mark it starts to bind on the rods, so this condition should be checked for when the brake is hard on.|
Another thing I forgot to mention in point 3 in my second post is that there is a limit to the amount of build-up possible as the lever still has to fit through the slot in the shoe. An small (~2mm) extension of the slot towards the inner edge of the shoe can usefully be done to allow a correspondingly better bearing surface.
I know that on one occasion I fitted the (rear) shoe the wrong way round (ie with the gap at the top rather than the leading end) as it better accommodated the built up nib. Just why it fitted better I can't remember! Both sides like this of course, and there didn't seem to be any adverse effect on the foot brake operation while the handbrake of course was much better.
Bill, we have a 1 in 3 driveway too, it's good for testing the handbrake on. As is the 20 metres of gravel on the flat bit at the top, where I can see if the skid marks from each wheel are uneven or not!
|Thanks Paul (+ Bill) for the input. I'll check out your ideas.|
This thread was discussed between 20/04/2013 and 22/04/2013
This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.